Typed crud values

[khawarizmus]

Following on foot steps of unifying our SDKs behavior. We should preserve the type of the CrudEntry.opData and CrudEntry.previousValues instead of returning a string. This was also reported on Discord

Related Issue: powersync-ja/powersync-kotlin#239

[simolus3]

We do actually have opDataTyped and previousValuesTyped now. opDataTyped is also mentioned in a documentation snippet already, so I think we can consider this done.